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Uncoupling of GPCR and RhoA‐induced Ca 2+ ‐sensitization of chicken amnion smooth muscle lacking CPI‐17
Author(s) -
Stevenson Andrá S.,
Matthew John D.,
Eto Masumi,
Luo Shizhen,
Somlyo Andrew P.,
Somlyo Avril V.
Publication year - 2004
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/j.febslet.2004.10.072
Subject(s) - rhoa , myosin light chain phosphatase , phosphorylation , microbiology and biotechnology , myosin light chain kinase , biology , protein kinase c , rho associated protein kinase , myosin , gq alpha subunit , g protein , signal transduction
Ca 2+ ‐sensitization of smooth muscle occurs through inhibition of myosin light chain phosphatase (MLCP) leading to an increase in the MLCK:MLCP activity ratio. MLCP is inhibited through phosphorylation of its regulatory subunit (MYPT‐1) following activation of the RhoA/Rho kinase (ROK) pathway or through phosphorylation of the PP1c inhibitory protein, CPI‐17, by PKC δ or ROK. Here, we explore the crosstalk between these two modes of MLCP inhibition in a smooth muscle of a natural CPI‐17 knockout, chicken amnion. GTPγS elicited Ca 2+ ‐sensitized force which was relaxed by GDI or Y‐27632, however, U46619, carbachol and phorbol ester failed to induce Ca 2+ ‐sensitized force, but were rescued by recombinant CPI‐17, and were sensitive to Y‐27632 inhibition. In the presence, but not absence, of CPI‐17, U46619 also significantly increased GTP · RhoA. There was no affect on MYPT‐1 phosphorylation at T695, however, T850 phosphorylation increased in response to GTPγS stimulation. Together, these data suggest a role for CPI‐17 upstream of RhoA activation possibly through activation of another PP1 family member targeted by CPI‐17.